On Tue, 23 Aug 2022 09:27:17 +0200, Takashi Iwai wrote: > > It's been reported that there is a possible data-race accessing to the > global card_requested[] array at ALSA sequencer core, which is used > for determining whether to call request_module() for the card or not. > This data race itself is almost harmless, as it might end up with one > extra request_module() call for the already loaded module at most. > But it's still better to fix. > > This patch addresses the possible data race of card_requested[] and > client_requested[] arrays by replacing them with bitmask. > It's an atomic operation and can work without locks. > > Reported-by: Abhishek Shah <abhishek.shah@xxxxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/r/CAEHB24_ay6YzARpA1zgCsE7=H9CSJJzux618E=Ka4h0YdKn=qA@xxxxxxxxxxxxxx > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Gah, there was an obvious type in the patch. The correct version is below, and I merged it now. thanks, Takashi -- 8< -- From: Takashi Iwai <tiwai@xxxxxxx> Subject: [PATCH v2] ALSA: seq: Fix data-race at module auto-loading It's been reported that there is a possible data-race accessing to the global card_requested[] array at ALSA sequencer core, which is used for determining whether to call request_module() for the card or not. This data race itself is almost harmless, as it might end up with one extra request_module() call for the already loaded module at most. But it's still better to fix. This patch addresses the possible data race of card_requested[] and client_requested[] arrays by replacing them with bitmask. It's an atomic operation and can work without locks. Reported-by: Abhishek Shah <abhishek.shah@xxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/CAEHB24_ay6YzARpA1zgCsE7=H9CSJJzux618E=Ka4h0YdKn=qA@xxxxxxxxxxxxxx Link: https://lore.kernel.org/r/20220823072717.1706-2-tiwai@xxxxxxx Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> --- v1->v2: fix compile error sound/core/seq/seq_clientmgr.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c index 2e9d695d336c..2d707afa1ef1 100644 --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -121,13 +121,13 @@ struct snd_seq_client *snd_seq_client_use_ptr(int clientid) spin_unlock_irqrestore(&clients_lock, flags); #ifdef CONFIG_MODULES if (!in_interrupt()) { - static char client_requested[SNDRV_SEQ_GLOBAL_CLIENTS]; - static char card_requested[SNDRV_CARDS]; + static DECLARE_BITMAP(client_requested, SNDRV_SEQ_GLOBAL_CLIENTS); + static DECLARE_BITMAP(card_requested, SNDRV_CARDS); + if (clientid < SNDRV_SEQ_GLOBAL_CLIENTS) { int idx; - if (!client_requested[clientid]) { - client_requested[clientid] = 1; + if (!test_and_set_bit(clientid, client_requested)) { for (idx = 0; idx < 15; idx++) { if (seq_client_load[idx] < 0) break; @@ -142,10 +142,8 @@ struct snd_seq_client *snd_seq_client_use_ptr(int clientid) int card = (clientid - SNDRV_SEQ_GLOBAL_CLIENTS) / SNDRV_SEQ_CLIENTS_PER_CARD; if (card < snd_ecards_limit) { - if (! card_requested[card]) { - card_requested[card] = 1; + if (!test_and_set_bit(card, card_requested)) snd_request_card(card); - } snd_seq_device_load_drivers(); } } -- 2.35.3